Underground excavation works in urban areas are frequently applied adjacent to existing structures and underground facilities, and they involve risks such as deformation of the surrounding ground due to excavation, groundwater degradation, and ground subsidence. In addition, as underground excavation becomes deeper, which increases lateral pressure on the retaining structure supporting the excavation surface, it is very important to secure the stability of the ground by restricting the wall displacement of the retaining structure and preparing measures for groundwater leakage.
In the urban vertical excavation work, the retaining wall system using Cast-In-Place Pile (C.I.P) and Secant Pile Wall (S.P.W) is mainly used. However, it is difficult to maintain the verticality of the conventional continuous pile wall system, which may lead to problems such as groundwater leakage and soil runoff due to poor continuity between piles.
In order to solve the problems of the conventional continuous pile wall system, a novel continuous pile wall system, called a Two-row Overlap Pile Wall System, with high flexural rigidity and waterproofing capacities for deep excavation support have been developed in South Korea. The Two-row Overlap Pile Wall System, constructed by tetra-axis auger(four-axis and two-row) has a shape and structure significantly different from that of other types of pile wall. Also, as the length of the overlapping of the cross-section or the number of a pile is changed, a large difference is shown in the cross-sectional shape and structural characteristics.
In this study, to obtain the basic data necessary to determine the optimum cross-section of the Two-row Overlap Pile Wall System, the flexural rigidity according to the cross-sectional structure and reinforcement condition is derived by both the theoretical and numerical method. In addition, the center-point loading flexural test was performed through using the scale model to evaluate the structural performance according to the cross-sectional condition of the Two-row Overlap Pile Wall System.
The results showed that the flexural rigidity tends to increase as the overlap length between piles decreases or as the number of piles increases from one column to two columns. Also, it was found that it has excellent flexural rigidity when compared with the conventional continuous pile wall system. Therefore, it is considered that Two-row Overlap Pile Wall system is suitable as a continuous pile wall for excavation surface support an excavation site.